In recent years, the use of wireless and RF technology has increased dramatically. The number of cellular telephone subscribers alone worldwide is expected to reach 3 billion by the end of 2008 according to the International Telecommunication Union (ITU). Similarly the devices incorporating wireless technology have expanded, and continue to so. It is anticipated that the overall market for other wireless devices will exceed cellular telephone units as consumers procure multiple devices per household.
Wireless devices interface to wireless infrastructures that support data, voice and other services via one or more standards. Some examples of wireless standards in significant deployment today include:                WiFi [ANSI/IEEE Standard 802.11];        WiMAX [IEEE Standard 802.16];        Bluetooth [IEEE Standard 802.15.1];        Industrial, Scientific and Medical (ISM) [International Telecommunications Union Recommendations 5.138, 5.150, and 5.280]; and        GSM 850/900/1800/1900 [European Telecommunications Standards Institute (ETSI)] and its extensions General Packet Radio Service (GPRS) and Enhanced Datarates for GSM Evolution (EDGE).        
Pricing of finished products is often a major factor in the commercial success of products. Accordingly, monolithic integration of the electronics to result in devices with low parts count—a small number of integrated circuits (ICs)—is common practice. In fact, a typical RF system will comprise a baseband controller IC, a radio receiver and transmitter, and an RF signal front-end that may include power amplifiers, low-noise amplifiers, switches, and filters amongst other possible signal conditioning blocks. These integrated circuits are manufactured using a silicon-based technology platform for baseband elements of the circuit that are ‘logic’ intensive and, typically from silicon germanium, gallium arsenide, and indium phosphide for many RF circuit elements that condition the incoming or outgoing radio signal primarily in the analog or RF domain. The RF circuit elements form a microwave circuit path from the RF signal mixers that are upconverting or downconverting the RF signals via amplifiers, microwave filters, circulators, etc. The RF signal is, of course, received from or transmitted to an RF antenna or other load such as a co-axial cable. An RF antenna or cable is an RF load for the transmitting circuit or RF signal front-end. Moreover, a collection of RF circuit elements might be manifested in the form of a monolithic microwave integrated circuit (MMIC) and may be part of the RF front-end in the form of a module.
Within many wireless consumer electronics products that are intended to receive or transmit information is a transmit/receive switch circuit that selectively connects a microwave transmission circuit to the RF load of the consumer electronics product and a microwave receiver circuit to the antenna or cable, such a switch circuit being a Single Pole Double Throw (SPDT) switch. The microwave transmission circuit and microwave receiver circuit are often a single bidirectional transmit/receive circuit. In other instances where the wireless consumer electronic product operates with multiple wireless standards there may be a separate microwave transmission circuit and microwave receiver circuit for each of the wireless standards supported. For example a wireless device supporting two wireless standards requiring different MMIC technologies for each, such as IEEE 802.11a at 5 GHz and IEEE 802.16 at 2.4 GHz, would have a Single Pole Quadruple Throw (SPQT) wherein a single common antenna or cable port is selectively coupled to one of two possible transmitter connections and a corresponding one of two receiver connections.
Conventionally, high-performance RF/microwave switches are implemented with depletion-mode GaAs MESFETs or PHEMTs. These devices are chosen because they offer very low Ron and Coff per unit gate width; these parameters determine switch insertion loss and isolation. The transistor is turned on by biasing Vgs>Vp, where Vp is the pinchoff voltage and Vp<0 for a depletion-mode device. The transistor is turned off by biasing Vgs<Vp, where a typical value of Vp might be −1.0 V. So Vgson might be 0 V and Vgsoff might be −2 V. This is accomplished, for example, by biasing the source and drain at 2 V and switching the gate to 0 V (off) or 2 V (on).
The D-mode GaAs FET or PHEMT has three major disadvantages for use as a high-performance switch. First is the tendency of gate current to flow when Vgs>0; the gate forms a Schottky diode to the channel which can turn on for large signal levels or inappropriate bias. Gate current flow leads to sharply increased loss and distortion in the switch. A second disadvantage is the absence of a complementary device type (p-channel FET); without a PFET, logic functions consume more power and die area. In some circuits it is difficult to control the switch using standard low-voltage CMOS levels. A third disadvantage is resulting higher die cost per unit area, which is aggravated by the relatively primitive and area-intensive ESD protection structures available in most GaAs FET processes.
Silicon-based RF/microwave switches that use the CMOS device as the core switch element are attractive because of the integration potential of combining both logic and RF functionality. In addition, the relatively low cost when compared to GaAs-based devices makes such Silicon-based RF/microwave switches attractive for the consumer electronics market. The conventional biasing arrangement and topology of an RF/microwave switch is, however, similar when the switch is manufactured using a Silicon-based CMOS technology or GaAs.
It is therefore a goal of the invention to overcome at least some of the limitations of the prior art.